Recently, opportunity to form a full color image is increasing in addition to conventional monochrome image using a toner for developing a static latent image (“toner”) in an image forming method via an electrophotography. The full color image forming method via an electrophotography is broadly used in a convenient printing field since necessary numbers of printed material can be manufactured on demand because of no printing plated is not necessary.
IT revolution commenced in 1990's introduces the circumstances of printing field to digital process markedly, RGB original has been normalized, and the data has been shifted to broader color reproduction area.
However, since full color image forming method by an electrophotography displays colors via subtractive color process by refractive light, color reproduction range is too small in comparison with display having a light source by itself via an additive color process, and therefore there is such a problem that it is difficult to reproduce a full color image shown on the display on a transfer material such as paper.
Particularly, there is a problem that color reproduction property of in high brightness region of secondary color prepared by overlapping two kinds of toners is poor. Practically, a toner image by yellow toner and a toner image cyan toner are superposed to reproduce green color, for example, chroma and brightness are reduced, and therefore color reproduction area of the green area becomes smaller than the color reproduction area via additive color process.
Therefore, toner giving minimized color turbidity and clear hue has been desired via subtractive color process in the full color image forming.
On the other side, for example, full color image forming method using six or more color toners including orange toner and green toner in addition to conventional four color toners composed of yellow toner, magenta toner, cyan toner and black toner is proposed as one of technologies to enlarge color reproduction area in the full color image forming method via subtractive color process. That is, hue represented through 360° by Munsell hue circle is not reproduced by three color toners of yellow toner, magenta toner and cyan toner, but color reproduction area is enlarged by using orange toner and green toner in addition to three color toners.
For example, green toner composed of non-metal phthalocyanine pigment and isoindoline type pigment in combination is proposed (for example, Patent Document 1).
However, the toner composed of non-metal phthalocyanine pigment and isoindoline type pigment in combination causes color turbidity, and chroma and brightness are not sufficient.
It is preferable to add another toner as green toner to improve brightness and chroma in green area, to yellow toner and cyan toner. For this purpose, green toner giving high brightness and chroma is required. However, green toner using existing green pigment is added, it is difficult to obtain green area color reproduction of sufficient brightness.